A broken rod tip-ring is pretty common, jamming the rod tip into something solid usually does the trick quickly and efficiently.
As usual the most efficient method of fixing a tip ring is to take it to a tackle shop who should fix it while you wait, and at no charge. But if you must go it alone, here is how:
If the tip ring itself is broken gently heat the tip with a cigarette lighter or match, and gently is absolutely critical, too much heat and you will soften then rod itself, and this is unrecoverable. Once the glue that holds on the tip is softened by the heat the rod tip should easily slide off.
Then using hot melt glue, melt some glue and rub it over the rod tip area, then slide on the new tip, make sure it lines up with the other guides and that is it – easy! (whatever glue you use, but I recommend hot melt glue, make sure the glue will release if the tip gets broken again).
If the rod tip is broken, clean up the tip to make sure there are no loose strands of fibreglass or graphite. Roughen up the rod tip where the new rod tip ring is to go with sandpaper, then glue on a new tip as covered above.